(1) Field of the Invention
The invention concerns a method and a device for monitoring at least one stability parameter of a loading crane mounted on a vehicle, wherein during crane operation the vehicle is or can be supported on the ground by means of wheels and by means of support elements separate from the wheels.
(2) Description of Related Art
Usually the support elements are support legs which can be extended in a vertical direction and which are mounted to a support extension which can be laterally extended in a horizontal direction. In that case the property of extendibility of the support legs and of the support extension is afforded by a telescopic structure. The vehicles which are relevant in connection with the invention generally have one or two such support extensions each having two support legs.
In accordance with standard EN 12999 an overload safety device for loading cranes with carrying capacities of over 1000 kg is required. In accordance with that standard the corresponding stability check is performed with a test load corresponding to 125% of the specified carrying capacity. What is important is that in that case at least one wheel which is braked by means of a parking brake (generally manually actuated) must remain on the ground. In that case the loading crane is in a so-called partially lifted condition. The at least one wheel which is braked by means of a parking brake and which must remain on the ground functions as an additional friction location and serves to carry horizontal forces.
It is known that the load moment limitation for the overload safety means in accordance with EN 12999 is resolved by means of lifting force adaptations in the crane hydraulic system. For crane operations with support elements which are not completely extended laterally and/or with boom positions beyond the driving cab additional lifting force limitations have to be implemented. Performance graph-based lifting force adaptations are part of the state of the art.
The high level of adjusting and checking complication and expenditure however is deemed a disadvantage in the case of such system solutions. There is the risk of maladjustments. In addition, no working loads are taken into account. To avoid those disadvantages preferably effects of crane operation on the overall machine are to be detected by a sensor system.
For truck-mounted concrete pumps there are approaches to such solutions, which point in that direction. By way of example DE 103 49 234 A1 is to be mentioned in this connection. Here, for monitoring stability, the support forces in the support legs are determined and calculated to give a stability index. It will be noted however that during operation thereof truck-mounted concrete pumps are in the fully lifted condition, that is to say, none of their wheels are resting on the ground. The solutions used for truck-mounted concrete pumps are therefore not suitable for the loading cranes which are relevant in connection with the present invention and which must comply with EN 12999.
Further approaches in regard to monitoring stability of a crane mounted on a vehicle are known from EP 2 298 689 A2, EP 1 757 739 A2 and EP 0 864 473 A2. None of those approaches can satisfy EN 12999.